Does Time Machine need a “clean drive”, or can I use an old hard diskBased on my experience with two separate TM backups on the same disk, the trimming part of TM works best and most fair if the disk space TM can use is fairly constant. The concrete case was that one backup grew large causing the other one to start discarding almost all the old backups to regain space. I ended up with losing a lot of history in one backup because the other backup grew too much.

IOS 7 iPad keyboard is unresponsiveAlso closing all other applications might release resources and make it less sluggish. Newer iPad models have more memory and Apple optimize the experience for them, so if you have an older model this might be the reason. A good example is that entering panorama mode on my iPhone 4S in iOS 7 might kill music playing instantly - my guess is that it requires SO much memory that even music playing (which should have top priority) has to go.